first off, if you're looking for good screenies, it's much better to take them from film viewer. when you do however, make sure that you set field of view zoom properly to minimise fisheyeing.
there is a bar to the right of the view window called FOV zoom that controls this. i usually take all my pictures with maximum FOV (bar set to the right). to turn on the fov zoom you need to press z key

anyway, about taking shots. get your shot set up, pause on the bit you like, set your views as you like. THEN, press the full screen button on the right of the viewer. adjust the full screen view so that you have you shot set up just as you like. then make sure that you move your mouse cursor out of the way (drag it off the screen) and hit the print screen button.
then fire up your editing software and paste the image, and save

hope that helps
